In flat or low-slope roofing applications, insulation boards are typically adhered directly to a roof deck, which is most commonly constructed using concrete or steel. The insulation boards are then covered with a weather resistant membrane. Efficiently adhering insulation boards to roof decks is accomplished by spraying an adhesive onto the roof deck and then applying insulation boards to the sprayed surface. Polyurethane is typically the adhesive of choice, where the term polyurethane refers to both those compounds including urethane bonds, isocyanurate bonds, or both.
Unfortunately, it is difficult to control the open time of polyurethane adhesives. Open time is the amount of time that the polyurethane has tack, which is an adhesive's ability to form chemical bonds with a substrate. Tack typically begins when the polyurethane reactants are contacted, and it ends when the reaction has gone to completion. Where the rate of reaction is fast, open time is typically very short. On the other hand, where the reaction rate is retarded or delayed, the open time can be extended, but insufficient tack and green strength are likely to result. This is problematic because tack and green strength are required for efficient insulation of the boards.